Help please!

I am a 20 year old female. I typically have regular period and have no issues. I am on the implant for birth control and have 17 days until my next period. Two days ago I have recently started a stool softener for some minor constipation. Yesterday I started to have dark brown discharge. Today while at work I had very dark brown discharge almost black. No cramps or any period symptoms. What is happening?!?